Brimonidine is neuroprotective against glutamate-induced neurotoxicity, oxidative stress, and hypoxia in purified rat retinal ganglion cells

PURPOSE: To investigate the neuroprotective effect of α2-adrenergic agonist brimonidine in the presence of glutamate-induced neurotoxicity, oxidative stress, and hypoxia on in vitro cultures of purified rat retinal ganglion cells (RGCs). METHODS: Purified RGC cultures were obtained from retinas of 6–8-day old Wistar rats, following a two-step immunopanning procedure. After 72 h of cultivation, the neuroprotective effect of brimonidine (0.01 μM, 0.1 μM, and 1 μM) was investigated by culturing the RGCs under glutamate, oxidative, and hypoxic stress for a further 72 h, 24 h, and 12 h, respectively. Glutamate neurotoxicity was induced by adding glutamate (25 μM), while oxidative stress was induced by substituting the culture medium with B27 supplement without antioxidants, and hypoxia was induced by cultivation in a controlled-atmosphere incubator with oxygen levels 5% of the normal partial pressure. The RGC viability under each stress condition normalized to that under normal condition was evaluated as live cell percentage based on a total of 7–8 full repeated experiments. RESULTS: The cell survival percentages of cultures exposed to glutamate, oxidative, and hypoxic stress were 58.2%, 59.3%, and 53.2%, respectively. Brimonidine dose dependently increased RGC survival in the presence of glutamate (80.6% at 1 µM), oxidative (79.8% at 1 µM), and hypoxic (72.3 and 77.4% at 0.1 and 1 µM, respectively) stress. In the presence of α2-adrenergic antagonist yohimbine (10 μM), brimonidine (1 μM) showed no protective effects on RGC viability. CONCLUSIONS: At a concentration of 0.1 µM or higher, brimonidine increased survival of purified rat RGCs in the presence of glutamate neurotoxicity, oxidative stress, and hypoxia. The neuroprotective effect of brimonidine is mediated via α2-adrenergic receptors at the RGC level.